1. Field of the Invention
The present invention relates to the sterilization of containers which are used in the beverage industry and particularly to improvements in techniques for ensuring that reusable barrels have been adequately cleaned and are free of leaks. More specifically, this invention is directed to improvements in and to a process wherein metal kegs are charged with a heated sterlilizing agent under pressure for the purpose of cleaning. Accordingly, the present invention is directed to novel and improved methods of such character.
2. Description of the Prior Art
In the beverage industry, it is common practice to employ reuseable containers, i.e., barrel like kegs, in the distribution chain between the brewer/bottler and the consumer. As is well known, such kegs have a screw-in fitting which includes an automatic shut-off valve. In order to ensure that the product in the keg will not degrade, a very high degree of container cleanliness must be achieved and maintained after each use. Thus, before being filled or refilled, the containers are sterilized, typically through the use of steam. The steam is introduced into the container under pressure and the container thereafter closed. The container, i.e., the keg, will be comprised of a metal such as stainless steel and the sterilization procedure will take place under ambient conditions. Accordingly, there will be a temperature differential across the keg wall and, accordingly, heat transfer through the wall of the keg. The internal temperature will fall as a result of this heat transfer and condensation of the steam will result. As the steam condenses, the pressure within the container will also fall. If the pressure within the keg falls below the ambient pressure, air will be sucked into the keg and sterility will be compromised. Thus, in the prior art, a pressure measurement is taken a predetermined time after the keg has been filled with steam and closed. The purpose of this pressure measurement is to exercise quality control over the sterilization process, and particularly to guarantee sterility, by determining whether there is a positive pressure in the keg after the waiting period.
In the conventional steam sterilization process as briefly described above, because of unrelated problems that may be encountered in the kegging plant, the waiting period varies from container to container, i.e., some kegs are kept under pressure longer than others. As the waiting period between steam pressure build-up and measuring the residual pressure increases, the pressure in the container steadily decreases because of the above-discussed temperature equalization with the surrounding air. It has been the previous practice in the art to simply determine whether or not the pressure within the keg is above the ambient atmospheric pressure. If the measured pressure is not positive, i.e., above ambient, the container is not filled. No more extensive analysis of the sterilization process is performed. There has, however, long been a need for providing more accurate information as to the quality of the sterilization process and the information desired should also be indicative of whether there are any leaks in the container.